Many industries and research facilities grow living cells for use in their manufacturing and research processes. Such cells may include microorganisms (such as bacteria, fungi, etc.) or cells from human, animal, plant, or other tissues. The cells are generally grown in vitro, and their environment is engineered to coerce the cells into producing some desired cell product, generally acids, enzymes, proteins, vitamins, bacteria, fungi, or other metabolic by-products, e.g., ethanol and penicillin, or more cells per se, e.g., yeast.
The prior art reveals various apparatuses for culturing cells and harvesting cell products produced by these cells. These apparatuses, frequently referred to in the art as bioreactors, include immobilized cell bioreactors wherein the cells to be cultured are immobilized by affixing them to components of the bioreactor. The cells are usually permanently or temporarily entrapped upon, within, or behind an immobilization matrix or membrane containing cell support surfaces, usually porous surfaces or surfaces having a gel or an electric field thereupon. A nutrient cell culture solution is supplied to the cell support surfaces so that the cells may feed upon it. As the cells feed upon the nutrient cell culture solution, they produce the desired cell product, generally either more cells or some cell byproduct. The nutrient cell culture solution (or some other carrier medium) carries the cell product and other cell wastes away from the cell support surfaces. The cell product may then be removed from the bioreactor in batches, or it may be removed continuously by collecting the cell product from the outgoing nutrient stream or from a separate cell product stream.
The prior art discloses a number of different types of bioreactors which utilize either continuous or batch processes to produce and harvest cells and cell products and which surround the immobilization matrices with either gas phase or liquid phase media. Several examples follow.
U.S. Pat. No. 4,665,027 to Dale et al. discloses a continuous immobilized cell bioreactor with two stages, an enricher stage and a stripper stage. In the enricher stage, gas and a liquid containing nutrient cell culture solution are continuously introduced into the bottom of the enricher, where they flow co-currently upward past cells immobilized on ceramic saddles. The cells produce volatile by-products which are absorbed into the gas, which exits to a condenser. The liquid is then continuously introduced into the top of a stripper stage where it flows downward past cells immobilized on ceramic saddles. At the same time, gas is introduced into the bottom of the stripper to flow upward counter-currently to the liquid. As it does so, the gas absorbs the volatile by-product produced by the immobilized cells. While the liquid flows from the bottom of the stripper, the gas is released from the top of the stripper to flow to the condenser. The condenser collects a continuous flow of by-product.
U.S. Pat. No. 5,079,168 to Amiot discloses a continuous gas phase bioreactor having an immobilization matrix comprising a gas-permeable but liquid-impermeable rolled cell support sheet. The cell support sheet is rolled with liquid-permeable capillaries separating each layer of cell support sheet within the roll. These capillaries transport nutrient cell culture solution and remove waste products.
PCT publication WO89/11529 to Wu et al. discloses a continuous liquid-phase bioreactor including an immobilization matrix comprised of parallel cell support sheets upon which a gel serves as the cell support medium. A liquid phase flows past and between the cell support sheets, collecting and transporting the cell product to be harvested.
The prior art also reveals a great variety of alternative immobilization matrix configurations and cell support media. For example, U.S. Pat. No. 4,789,634 to Muller-Lierheim et al. discloses an immobilization matrix comprising a pressure resistant polymer bead matrix wherein the interstitial spaces between beads entrap and harbor the microorganisms. Capillaries within the beads allow for distribution of nutrient cell culture solution to the microorganisms, but do not allow the microorganisms to grow within the beads. The same reference also discloses an immobilization matrix made of sheets of beads organized in a parallel layered fashion.
Another example of an immobilization matrix is disclosed in U.S. Pat. No. 4,689,301 to Adet et al. This reference discloses a cell support medium comprising a transparent polyurethane foam cell support sheet. Microorganisms are harbored within pores in the sheet wall, and nutrient cell culture solution is supplied to the cell support sheet to feed the immobilized cells. Adet et al. also reveal a parallel layered arrangement of sheets.
U.S. Pat. No. 4,925,803 to Suehiro et al. discloses an immobilization matrix comprising a braided configuration of long, tubular filaments which is then rolled onto a tubular frame. The microorganisms become entrapped within the immobilization matrix, and nutrient cell culture solution is supplied in the axial direction through the frame.
Thus, the prior art shows a number of immobilized cell bioreactors involving parallel arrays of cell support media, some of which are gas phase and some of which are liquid phase. However, all bioreactors in the prior art tend to be quite complex and expensive. First, the immobilization matrix tends to be made of specialized cell support media utilizing surface gels or precision-engineered surfaces including pores, capillaries, or interstitial spaces. Second, all bioreactors in the prior art tend to require expensive transport mechanisms which use pumps or other specialized equipment to transport the cell product and/or nutrient cell culture solution away from the immobilization matrix.